1. Field of the Invention
This invention relates to a skin used to form a surface such as a vehicle interior panel and manufacturing method thereof, and to a manufacturing method of skin for air bag door and an air bag door.
2. Related Art
For protecting passenger in an automobile from a traffic accident with increase of the traffic, an air bag has been installed in the recent automobile. For example, the air bag for a driver contained in a steering wheel is expanded by gas generated due to shock applied in collision of the automobile and developed in to a vehicle room. Thus, the air bag protects the driver seated on a driver's seat from collision against the steering wheel and a front glass. The air bag may also has been contained in a rear surface side of an instrument panel to protect a passenger seated on an assistant seat from collision against the instrument panel and the front glass. Further, in recent years, installing the air bag in a rear surface side of a door trim to protect the passenger from collision applied from side (door) has been recommended.
The vehicle interior panel such as the instrument panel and the door trim are constructed by a base member made of a hard resin, a foamed body layer made of a polyurethane foam etc. and laminated on a surface of the base member, and a skin made of a polyvinylchloride etc. and laminated on a surface of the foamed body layer. The interior panel holds shape thereof by rigidity of the base member, increases smooth feeling by the foamed body layer, and increases surface appearance and further increases the smooth feeling by the skin.
When the air bag is disposed in the rear surface side of such interior panel, the interior panel having rigidity is hardly broken to hinder the expansion and development of the air bag. In view of this, the interior panel is provided with an opening usually closed or covered by an air bag door and allows the air bag to develop. When the air bag expands by large shock applied to the automobile by collision etc., the air bag door is pushed and opened by the air bag for allowing the air bag to develops into the vehicle room smoothly.
Conventionally, the air bag door is formed separately or independent from the interior panel, and is fixed to the interior panel by engagement and so on. According to such separate air bag door construction, the interior panel does not hinder development of the air bag into the vehicle room. However, in this case, a boundary line (outer periphery) of the air bag door may appear on the surface of the interior panel as a relatively wide and deep groove, or a step or height difference may be formed between the interior panel surface and the air bag door surface, whereby the surface appearance of the interior panel is deteriorated in both cases.
On the other hand, if the air bag door is formed integral with the interior panel, the boundary line of the air bag door does not appear or expose on the surface of the interior panel to improve the surface appearance thereof. However, such integral structure may hinder development of the air bag into the vehicle room, so that connecting strength of the air bag door with the interior panel needs to be selected as small as possible for an instantaneous development of the air bag when the shock is applied.
As such interior panels having small connecting strength of the air bag door, Japanese Patent Publication No. 1-202550 for example discloses a cover body for an air bag comprising a core layer made of a hard resin and provided with a slit of H-shape or cross-shape, and a soft skin layer formed on a surface of the core layer integral therewith.
Also, Japanese Patent Publication No. 5-294196 discloses an air bag containing cover body comprised of a hard core layer provided with a slit at a rear surface side thereof, and a soft skin layer.
In these interior panels disclosed in the above Publications, in the usual state when the shock is not applied, rigidity of the interior panel is secured by the core layer, and the smooth feeling is obtained by the skin layer. When the shock is applied, the cover body is torn along the slit on the core layer forming a fragile portion by the expanding force of the air bag and allows the air bag to develop into the vehicle room.
However, even when the fragile portion is provided on the core layer so that part of the core layer defined by the fragile portion forms the door, there is case where an extensive rigidity of the skin layer hinders development of the air bag. In view of this, Japanese Patent Publication No. 7-156737 discloses an air bag structure in which a skin of an air bag door and a skin of an interior panel are separately formed, and a convex portion and a concave portion provided on annular bent flanges of the both skins are engaged with each other to form an integrated skin. This integrated skin is disposed in a mold, followed by an integral forming of a foamed body layer to the skin. This air bag structure hardly generates a step or a gap at the boundary portion of the air bag door, and will not cause problem due to the extension rigidity of the skin. Japanese Patent Publication No. 11-222089 discloses a skin for an instrument panel comprised of a general portion and an air bag door portion formed at a part of the general portion and defined by an annular groove portion. In this skin, the air bag door portion and the general portion are formed so that a step portion is formed between the surface of the former and the surface of the latter, and opposing peripheries of the air bag door portion and the general portion are coincided in a direction parallel to the surface of the skin.
The groove portion of the skin for the instrument panel is deformed by relative shift of the air bag door portion and the general portion in the direction orthogonal to the skin surface to remove the step portion, then is set in the foam mold together with the resin base member. Then, the foamed body layer is formed by the foam forming to connect it with the base member and the skin integrally. Thus, the instrument panel having the air bag door can be produced.
According to the skin for the instrument panel of Japanese Patent Publication No. 11-222089, the surface appearance of the skin can be improved due to the narrowed width of the groove portion. Also, the man-hour for forming the skin for the instrument panel can be reduced since the skin having the air bag door portion can be formed by single forming process. Further, durability of the mold for the skin increases since thickness of the convex portion on the mold for forming the groove portion needs not be thinned extremely.
However, the above Japanese Patent Publication No. 7-156737 and Japanese Patent Publication No. 11-222089 have following disadvantages. That is, in the interior panel construction shown in the above JP '737, the skin of the air bag door and the skin of the interior panel needs to be separately formed, which requires the separate, two kinds of molds, and increases the manufacturing cost of the skin. Also, the connecting working between the skin of the air bag door with the skin of the interior panel increases the required man-hour. Further, to prevent formation of the step portion and the gap which may be formed at the boundary portion of the air bag door when the air bag door and the interior panel are connected, the convex portion and the concave portion formed at the annular flanges of the skins should have high positional accuracy. To set the tearing condition of the skin in the expansion of the air bag constant, the convex portion and the concave portion of the annular flanges should have high shape accuracy. These accuracy requirements also increase the man-hour.
Also, in the skin for the instrument panel disclosed in the above JP '089, the groove portion has the depth direction extending orthogonal to the skin surface. For this reason, if the groove portion is opened in the endurance test or after long-term use, the deeper part of the groove appears remarkably. Further, the instrument panel is formed in the condition where the groove portion is deformed, the stress generated by deformation of the groove portion remains in the skin to cause deformation of the skin.